Contribución de la fotogrametría al estudio de la evolución de un sector del caño mareal del Río San Pedro (Bahía de Cádiz, España)

Using historical aerial photographs we can go back in time and perceive landscape features in earlier phases of development. The digital processing techniques together with the Internet access to the photogrammetric databases recently generated by some institutions provide a powerful tool for studying dynamic phenomena. This paper presents an application of photogrammetric techniques to study the change in the tidal channel of Rio San Pedro, near its mouth in the Cadiz Bay. The study is based on analysis and comparison of 10 orthophotos from flights made between 1956 and 2010. The major phenomenon affecting that stretch of canal is quantified. It is the lateral migration of the channel to the SE (between 1.15 and 1.4 m / year). This phenomenon leads to the recoil of erosional escarpment that bounds the backshore (between 0.5 and 0.25 m / year), consisting of a aeolian sands formation fixed with vegetation, which is the main source of sand to the channel. The lower rate of recoil of erosional escarpment compared to channel migration produces a change in the slope and width of the intertidal zone and an activation of dynamism.